Key Technical Points for Freeze Prevention in Winter Temporary Holding of River Crabs

1. Breaking the ice  

Commercial crabs are held temporarily at high density, and after snow the temperature is relatively low, making aquaculture management more difficult. By opening ice holes or breaking the ice, on the one hand you can observe whether the overwintering pond is short of water or oxygen, and on the other hand, some harmful gases in the water body can escape. When oxygen in the water is low (below 1.8mg/L), cyclops, water fleas and other aquatic insects can be seen gathering near the ice holes; take timely oxygenation measures according to what you observe.

2. Oxygenation   85% of the oxygen in the water comes from photosynthesis by phytoplankton, and a small part comes from dissolution from the air and from water added to top up the pond.

1) Keep the ice clear   The overwintering pond should freeze with clear ice. If it freezes into dark ice, break it and let it freeze again, ensuring clear ice covers more than 50% of the area. After snow, clear the snow promptly, clearing more than 80% of the pond area. If the dark ice is not removed or the snow is not swept in time, light under the ice will be insufficient, photosynthesis will be blocked, and oxygen deficiency easily results.

2) Mechanical oxygenation   A 1.5-3.0 kW aerator can be run continuously for 2-3 hours for oxygenation. When the overwintering pond is short of oxygen and also lacks a water source, a water pump can be used for circulating water oxygenation. An air cylinder or air pump can also be used to force air into the water for oxygenation.

3) Chemical oxygenation   In emergencies, chemical agents such as Zengyangling can be used for oxygenation.

3. Adding water  

Ensure the water depth under the ice in the overwintering pond is above 0.8m. If it is below this, add water at any time to top it up. The temperature of the added water must exceed 4°C.

4. Harvesting  

Above 0°C, the pond can be drained for catching; below 0°C, catching is not advisable, and water can be let into the crab pond. Specific method: drain the pond to catch crabs during the day, and let water back into the crab pond in the evening.